FIG. 1 is a cross-sectional view showing the basic construction of a multiplate clutch 10 in which friction plates are used. The drawing shows a clutch case 1, friction plates 2, separator plates 3, a piston 4, a backing plate 5, and a stopper ring 6. The friction plates 2 are connected to a hub (not shown) through splines, while the separator plates 3 are connected to the clutch case 1 through splines. An alternate long and short dash line X-X indicates a central axis.
To bring the clutch into engagement, pressure oil is introduced between the clutch case 1 and the piston 4 such that against the backing plate 5 held in place by the stopper ring 6, the friction plates 2 and separator plates 3 are pressed via the piston 4. As a consequence, a torque is transmitted between the clutch case 1 and the unillustrated hub.
FIG. 13 is a front view illustrating one example of conventional friction plate constructions (see, for example, Fujimoto, et al. U.S. Pat. No. 5,094,331, JP-A-50-30145[U], and JP-A-01-146019[U]). A friction plate 2 is formed of a metal plate, as a core plate 21, and friction linings 25 bonded on opposite surfaces of the core plate 21, respectively. Designated at numeral 24 are splines through which the friction plate 2 is connected to an unillustrated hub. To facilitate flowing of lube oil into each friction lining 25 so that the friction lining 25 can be cooled with the lube oil, the friction lining 25 is provided with oilways 28 and oil grooves 29. The oilways 28 communicate to both inner and outer circumferential walls of the friction lining 25, while the oil grooves 29 are open only in the inner circumferential wall of the friction lining 25.
In machinery, there is an outstanding desire for still higher power output, still higher efficiency and further reductions in size. Friction plates for use in such machinery develop an inconvenience that the cooling of their friction linings is not sufficient insofar as they are constructed by simply arranging oilways and oil grooves in their friction linings as in the conventional art. A need, therefore, has arisen to achieve a further improvement in the cooling performance for friction linings.